The movement to more-electric aircraft (MEA) architectures during the past decade in military and commercial aircraft systems continues to increase the complexity of designing and specifying the electric power system (EPS). The addition of numerous high-power electric loads has drastically altered the dynamics of power flow on the electrical bus. Such loads include electro-hydrostatic actuators (EHAs), electromechanical actuators (EMAs), advanced radar, and directed energy weapons (DEW). Although these loads represent a relatively small portion of the average power draw from the EPS, the short-term transient power may exceed twice the average power capabilities of the generator, with peak-to-average power ratios in excess of 5-to-1 for brief periods of time (50-5000 ms). In addition to this high peak-power, some of the loads can produce regenerative power flow during deceleration of motors and drive trains which is equal to peak power draw for brief periods of time (typically 20-200 ms).
There exists a wide variety of architectures which are capable of addressing the challenges of this dynamic power profile. For example, one architecture is to force regenerative power to be handled locally with diodes and/or power resistors and to size the generator (including the gearbox, shafts, etc.) to be capable of peak power generation. Such architecture can be challenging to design and may lead to an unnecessarily large increase in system weight due to increased demands on the thermal systems and derating of key mechanical components in the generator drive-train.
Another viable approach is to allow the electrical bus to support bidirectional power flow all the way back to the engine. Aircraft generators often already have the requisite power electronics to support bi-directional power flow due to their dual role of providing main-engine start capability. While this approach reduces the thermal concerns associated with burning regenerative power locally, it actually increases the derating factors required in the mechanical drive-train of the generator which again could result in increased system weight. In addition, such architecture requires all sources (i.e. emergency power units, auxiliary power units, battery, and ground power carts) to support bi-directional power flow. The resulting increase in size, weight and cost associated with these sources may be unacceptable in relation to the system design and cost constraints. A need exists for an improved design which increases the load-handling capabilities of the aircraft electric power system while minimizing the weight and size requirements of the associated components.